Apparatus for radiating sound waves



Nov. 4, 1930. R. D. FAY

APPARATUS FOR RADIATING SOUND WAVES Filed Dec. 10, 1927 5 Sheets-Sheet lNov. 4, 1930. R. D, FAY 1,780,349

APPARATUS FOR RADIATING SOUND WAVES Filed Dec. 10, 1927 V 5 Sheets-Sheet2 Nov. 4, 1930. R. FAY

APPARATUS FOR RADIATING SOUND WAVES Filed Dec. 10, 1927 5 Sheets-Sheet 4N QQ I JJENTU ATTEIRNEI'L:

Ndv. 4, 1930. R, D, FAY 1,780,349

APPARATUS FOR RADIATING SOUND WAVES Filed Dec. l0, 1927 5 Sheets-Sheet 5B ATTEI H EL! Patented Nov. 4, 1930 PATENT OFFICE RICHARD D. FAY, 0FCAMBRIDGE, MASSACHUSETTS APPARATUS FOR RADIATING SOUND WAVES Applicationfiled December 10, 1927. Serial No. 239,178.

distinct iron circuits, one of which carries a constant magnetic flux,and the other a varia'ble flux, said constant magnetic flux passingthrough a portion or portions of said armature normal to the planethereof.

stant magnetic field, and an armature which is preferably a closedelectric circuit resiliently suspended in a gap across which saidconstant magnetic flux flows normal to the plane of said conductor, acoil or winding energized by variable currents such as those of theoutput circuit of the tube in the last audio stage of a radio receivingset, said coil being inductively related to said. closed conductor and atympanum suchyas a cone supported, preferably, only at its apex on saidclosed electric circuit, whereby a force will be exerted on said closedelectric circuit perpendicular to the constant magnetic flux and thecurrent induced in said closed electric circuit by the variable currentsin said winding, said force being proportional tosuch induced current.

An illustrative embodiment of my invention is shown in the accompanyingdrawings in which c Figure 1 is, a plan view ofa radio loud speakerembodying my invention;

Figure 2 is a vertical elevation;

Figure 3 is a horizontal section taken on the liine 33 of Fig. 2;

Figure 1 is a longitudinal vertical section taken on the line 414 ofFigure 1;

Figure 5 is a transverse vertical section taken on the line 5-5 of Fig.2; and

Figure 6 is a fragmentary sectional view showing one wayin which thetympanum can be mounted on the armature.

In the illustrative embodiment of my inventlon shown in the accompanyingdrawings, 10 represents a base carrying at its opposite ends thebrackets 11, secured to which are the oppositely-disposed permanent orhorse-shoe magnets 12, the juxtaposed ends of which are separated bynarrow gaps and are maintained in fixed relative position by thenon-magnetic plates 13 attached to the outer faces thereof, and thebolts 13 pass- My invention contemplates the use of permanent orelectromagnets for creating a con-i ing transversely through the legs ofthe magnet. 7

It will be understood of course that electromagnets may be employed inplace of the permanent magnets illustrated.

A pair of brackets 14 are secured to the opposite sides of the base forsupporting the closed laminated core 15 of a transformer,

the primary of which consists of the coils 16 and the, secondary of theclosed electrical circuit 17, shown in the present instance as a thinrectangular copper plate having its center'portionremoved so as to forma single turn of conductor closed on itself. The secondary 17 is inclose inductive relation to the primary 16. A transformer of this typeis generally known as a closely-coupled transformer. h

Obviously a variety. of means may be employed for supporting the saidtransformer in the proper position with respect to the other elements ofthe system, and that I do not limit myself to the means specificallyshown and described.

In the present instance, two parallel vertical plates 18 separated apartby the blocks 19 are attached to the brackets 14 by the screws 20, andthe laminations of said core 15, which preferably are of the E-type arethreaded through the primary windings 16, and the closed circuitsecondary 17 until the core has been built up to the desired size,whereupon the said laminations are clamped together by the bolts 22 andbars 21 which are then secured in adjusted position to said plates 18 bythe bolts 23.

The closed circuit secondary 17 is suspended preferably resiliently inthe gaps between the permanent magnets by three sets of filaments 24 ofresilient material, such as bronze, which, as indicated in Figs. 2 and4, may pass through holes near the edge of said secondary, preferablymaking a turn through said holes, and then around the tightening screws25, after passing through notches 26 in the plates 27 which are securedto the inner sides of the brackets 14.

It is quite essential that said filamentary suspensions be maintained inparallel relation each with the others on the same side i of thesecondary or armature 17, to allow maximum freedom of motion thereof.

Secured to, or as shown, preferably integral with the secondary 17, aretwo forwardly-projecting members to which the bakelite yoke 28 issuitably attached, as by molding the same thereto, and molded to saidyoke is a horizontally-disposed threaded stud 29 to which the tympanumshown in Fig. 6 as a cone 30, may be attached in any suitable manner.

It will be noted that at least one portion, and preferably twooppositely disposed portions of the closed circuit secondary 17, viz,the upright sides thereof, lie in the gaps between the magnets 12, andalso that the primary windings 16 are outside the field of saidpermanent magnets, in order to reduce the gaps between the magnets 12 toa practicable length. If the primary windings were not outside the fieldof the permanent magnets, it would be necessary to have a gap of suchgreat length that it would be impossible to maintain a field ofsuificient strength to give effective results.

There is, therefore, a magnetic circuit, namely, that of the permanentmagnets, carrying a constant magnetic flux, and a second independentclosed magnetic circuit, namely, the core 15 of the transformer 16 17,in which a variable magnetic flux is created by the variable currentsenergizing the primary of the transformer. The said variable magneticflux induces currents in the closed secondary 17 which, being suspendedin the path of the constant magnetic flux, will be given a vibratorymotion in the direction of its plane, that is to say, will moveedgewise, against the tension of the filamentary suspension members.While the system is 5 mounted to allow such edgewise motion,

there is great restriction to any other form of motion.

It will be observed that the closed circuit secondary constitutes anextremely light rigid armature which has no electrical or magneticcontact with the rest of the system, that said secondary has very lowinductive reactance, that a comparatively small magneto-motive force isrequired to maintain the field, because no insulation material isrequired in the gap, that the suspension members ma be extremely light,because there is no orce other than the working force and gravity on themoving sys tem, that the disposition of the parts allows a closed ironcore for the transformer which carries no permanent fluX, and hencesuffers no loss of permeability, and that there are two separate anddistinct iron circuits, one carrying a constant magnetic flux and theother, which is in effect the core of a transformer, carrying a variableflux, all of which features make for simplification and efficiency andalso fidelity of reproduction.

Having thus described an illustrative embodiment of my invention withouthowever limiting the same thereto, what I claim and desire to secure byLetters Patent is:

1. A sound-radiating device comprising in combination, means creating aconstant magnetic field having two oppositely-disposed gaps, a primarywinding without said field, a closed secondary inductively related tosaid primary and having two oppositelydisposed portions thereof locatedwithin said gaps, means suspending said secondary for motion in thedirection of its plane, and a tympanum secured to said secondary.

2. A sound-radiating device comprising in combination, a magneticcircuit carrying a constant magnetic flux, a closed magnetic circuitmagnetically independent of the firstmentioned magnetic circuit, meanscreating a variable magnetic flux in said closed magnetic circuit, aclosed electric circuit suspended in the path of said constant magneticflux and linked by said variable magnetic flux, and a tympanum securedto said closed electric circuit.

3. A sound-radiating device comprising in combination a winding, aconductor closed on itself and inductively related to said winding, asuspension for said. conductor, said suspension comprising a pluralityof filaments of resilient material attached, respectively, to theopposite sides of said conductor, means for variably tensioning saidfilaments,means creating a constant magnetic flux passing through aportion of said conductor normal to the plane thereof and a tympanumsecured to said conductor.

4. An electromagnetic mechanism comprising in combination means forcreating a constant magnetic field, a closely coupled transformerhavinga closed magnetic circuit independent of said field, a primarywinding Without said field and a closed secondary in close inductiverelation to said primary,a portion of said secondary being locatedWithin said magnetic field, and means suspending said secondary formotion in the direction of its plane.

' In testimony whereof, I have hereunto subscribed my name this 9th dayof December, 1927.

RICHARD D. FAY.

